While on one airline passengers may be used to boarding first if they’re seated towards the front of the plane, they may find themselves last on the plane on a different airline. Those who care deeply about overhead space and being able to settle in before the flight takes off should pay attention.

Here’s how you can expect to board with major American airlines.

American Airlines

American Airlines has nine different boarding groups, numbered in ascending order. Groups one through four are passengers seated in first or business classes, with frequent flier status, or in the military.

Group five begins with “Main Cabin Extra” and then continues to group eight for the main cabin. These groups to board are organized by zone on the airplane. The last to board is group nine: basic economy. Those in the last group won’t have any room in the overhead compartment — but, then again, one rule of the basic economy ticket is that passengers aren’t allotted a carry-on item.

Delta

Delta has a boarding style typical of most U.S. airlines. Boarding starts with customers needing extra assistance, then moves on to first class, frequent fliers and passengers with rewards credit cards. Afterwards the floodgates open for the main cabin passengers, boarding the plane from the rear to the front. Last to board are basic economy customers. Although they are allowed one carry-on, by the time basic economy boards it is likely that overhead compartments will be full and passengers will have to check their bags at the gate.

United

United’s boarding process starts off fairly normal: pre-boarding for military, unaccompanied minors and anybody who needs extra time. Group one boarding is for those in premier classes while group two are passengers with frequent flier status. But then things start to change.

Passengers in the main cabin will board window seats first (group 3), then middle (group 4) and finally the aisles (group 5). So those who prefer easy access to the aisle during their flight may find themselves without room in the overhead compartment when they finally board.

Southwest

Southwest is (in)famous for its unique boarding procedure. When passengers get an email that it’s time to check in for their flight, they should follow the link immediately and check in ASAP. Passengers that check in first get on the plane first. The boarding groups are A, B and C — with each passenger assigned a number somewhere in that group. When the gate agent calls your group number, you find your place in line. Business Select tickets will get to board first (they are always A 1-15). Once on the plane, there is open seating.

Alaska (and Virgin)

Alaska’s boarding process starts with pre-boarding (military, families with young children, those who need extra time) and then moves on to first class customers. Frequent fliers and those who have purchased premium boarding are up next.

General boarding are the last two groups, starting with those seated behind the exit rows.

Frontier

Frontier’s boarding process may seem a bit different as a budget airline, however it’s still fairly similar to industry standards. Those who need extra time board first. Then it’s people who paid a fee to board early. Frontier charges for overhead bin access. Those who choose to pay the extra fee for a carry-on can board before the rest of the cabin. Then it’s boarding from back to front. Seats (and boarding zones) are randomly assigned — unless a passenger chooses to pay an extra fee.

Spirit

Spirit is known for its extra fees. Those who pay those fees are able to get on the plane first — except for unaccompanied minors or passengers who require assistance. Passengers who purchased “big front seats” are allowed to board first and then the remaining rows (from front to back) are allowed onto the plane. Passengers who pay for seat assignment can choose a seat towards the front of the plane to board first.